Seungwoo Park

CD44-positive cells are responsible for gemcitabine resistance in pancreatic cancer cells

Accumulating evidence suggests that tumors are composed of a heterogeneous cell population with a small subset of cancer stem cells (CSCs) that sustain tumor formation and growth. Recently, there have been efforts to explain drug resistance of cancer cells based on the concept of CSCs having an intrinsic detoxifying mechanism. In the present study, to investigate the role of CSCs in acquiring chemoresistance in pancreatic cancer, gemcitabine‐resistant cells were established by exposure to serially escalated doses of gemcitabine in HPAC and CFPAC‐1 cells. Gemcitabine‐resistant cells were more tumorigenic in vitro and in vivo, and had greater sphere‐forming activity than parental cells. After high‐dose gemcitabine treatment to eliminate most of the cells, CD44+ cells proliferated and reconstituted the population of resistant cells. CD44+CD24+ESA+ cells remained as a small subset in the resistant cell population. Among ATP‐binding cassette (ABC) transporters, which are known as the mechanism of drug resistance in CSCs, ABCB1 (MDR1) was significantly augmented during the acquisition of drug resistance. ABC transporter inhibitor verapamil resensitized the resistant cells to gemcitabine in a dose‐dependent manner and RNA interference of CD44 inhibited the clonogenic activity of resistant cells. In human pancreatic cancer samples, CD44 expression was correlated with histologic grade and the patients with CD44‐positive tumors showed poor prognosis. These data indicate that cancer stem‐like cells were expanded during the acquisition of gemcitabine resistance and in therapeutic application, targeted therapy against the CD44 or ABC transporter inhibitors could be applied to overcome drug resistance in the treatment of pancreatic cancer.

A Hypoxia-Induced Vascular Endothelial-to-Mesenchymal Transition in Development of Radiation-Induced Pulmonary Fibrosis

Purpose: Radiation-induced pulmonary fibrosis (RIPF) is a late side effect of thoracic radiotherapy. The purpose of our study was to gain further insight into the development of RIPF. Experimental Design/Results: Here, we observed that irradiation of mouse lungs induced collagen deposition, particularly around blood vessels, in the early phase of RIPF. Such deposition subsequently became evident throughout the irradiated tissues. Accompanied by the collagen deposition, vascular EndMT (endothelial-to-mesenchymal transition) began to develop in the early phase of RIPF, before the appearance of EMT (epithelial-to-mesenchymal transition) of alveolar epithelial (AE) II cells in the substantive fibrotic phase. Concomitant with the EndMT, we detected vascular endothelial cell (EC)–specific hypoxic damage in the irradiated lung tissues. In human pulmonary artery endothelial cells (HPAEC), the radiation-induced EndMT via activation of TGFβ-R1/Smad signaling was dependent on HIF1α expression. A novel HIF1α inhibitor, 2-methoxyestradiol (2-ME), inhibited the irradiation-induced EndMT via downregulation of HIF1α-dependent Smad signaling. In vivo, 2-ME inhibited the vascular EndMT, and decreased the collagen deposition associated with RIPF. Furthermore, HIF1α-related EndMT was observed also in human RIPF tissues. Conclusions: We provide the first evidence that an EndMT occurs in RIPF development and that the EndMT may be effectively inhibited by modulating vascular EC-specific hypoxic damage. Clin Cancer Res; 21(16); 3716–26. ©2015 AACR.

Paclitaxel augments cytotoxic effect of photodynamic therapy using verteporfin in gastric and bile duct cancer cells

Photodynamic therapy (PDT) shows a limited antitumor effect in treating gastrointestinal tumors because of improper light penetration or insufficient photosensitizer uptake. The aim of this study was to evaluate the cytotoxic effect of PDT combined with paclitaxel on in vitro cancer cells. In vitro photodynamic therapy was performed in gastric cancer cells (NCI-N87) and bile duct cancer cells (YGIC-6B) using verteporfin (2 ug mL(-1)) and a PTH light source (1 000 W, Oriel Co.) with 665-675 nm narrow band pass filter. Cytotoxicity was compared using the MTT assay between cancer cells treated with PDT alone or pretreated with paclitaxel (IC(25)). Apoptotic changes were evaluated using DAPI staining, DNA fragmentation analysis, Annexin V-FITC apoptosis assay, cell cycle analysis, and western blots for cytochrome c, Bax, and Bid. The PDT-induced cytotoxicity was potentiated by pretreating with low dose paclitaxel (P < 0.001). The enhanced cytotoxicity was due to an augmented apoptotic response mediated by exaggerated cytochrome c released from mitochondria, without Bax or Bid activation. These results show that paclitaxel pretreatment enhances PDT-mediated cancer therapy.

HSPB1 Inhibits the Endothelial-to-Mesenchymal Transition to Suppress Pulmonary Fibrosis and Lung Tumorigenesis.

The endothelial-to-mesenchymal transition (EndMT) contributes to cancer, fibrosis, and other pathologic processes. However, the underlying mechanisms are poorly understood. Endothelial HSP1 (HSPB1) protects against cellular stress and has been implicated in cancer progression and pulmonary fibrosis. In this study, we investigated the role of HSPB1 in mediating the EndMT during the development of pulmonary fibrosis and lung cancer. HSPB1 silencing in human pulmonary endothelial cells accelerated emergence of the fibrotic phenotype after treatment with TGFβ or other cytokines linked to pulmonary fibrosis, suggesting that HSPB1 maintains endothelial cell identity. In mice, endothelial-specific overexpression of HSPB1 was sufficient to inhibit pulmonary fibrosis by blocking the EndMT. Conversely, HSPB1 depletion in a mouse model of lung tumorigenesis induced the EndMT. In clinical specimens of non-small cell lung cancer, HSPB1 expression was absent from tumor endothelial cells undergoing the EndMT. Our results showed that HSPB1 regulated the EndMT in lung fibrosis and cancer, suggesting that HSPB1-targeted therapeutic strategies may be applicable for treating an array of fibrotic diseases.

Signet Ring Cell Carcinoma of the Extrahepatic Bile Duct

Most tumors affecting the extrahepatic bile duct are adenocarcinomas; the other histologic types occur only rarely. We herein report the extremely rare case of signet ring cell carcinoma (SRCC) originating from the extrahepatic bile duct. A 55-year-old man was hospitalized for jaundice and pruritus. Computed tomography and positron emission tomography suggested the presence of distal extrahepatic bile-duct cancer. He underwent a pylorus preserving pancreaticoduodenectomy. A histologic study confirmed a signet ring cell neoplasm of the distal common bile duct. Because the upper resection margin was invaded by the tumor, he received postoperative concurrent chemoradiotherapy and four cycles of chemotherapy. The patient has survived with no evidence of recurrence for 2 years. This is the second case of primary SRCC of the distal extrahepatic bile duct reported in the literature; further reports of cases are warranted to determine the nature of SRCC in the extrahepatic bile duct.

Role of HLA class II alleles in Korean patients with IDDM

MHC associations with IDDM in the Korean population were studied to investigate genetic susceptibility to this disorder. The frequencies of HLA-DR3, -DR4 and -DR9 were significantly higher in diabetic patients. However, the frequency of DR2 was significantly decreased in diabetic patients. DQA1*0301 and DQA1*0501 were positively and DQA1*0102 and DQA1*0201 negatively associated with IDDM. DQB1*0301 and DQB1*0601 were negatively associated with IDDM. Heterodimers DQA1*0301-DQB1*0201, DQA1*0501-DQB1*0201 and DQA1*0501-DQB1*0302 were positively associated with DQA1*0102-DQB1*0601 negatively associated with IDDM. The frequencies of DR3-DQA1*0301-DQB1*0201 and -DQA1*0501-DQB1*0201 were significantly higher in diabetic patients. The frequencies of DR4-DQA1*0301-DQB1*0201 and DR9-DQA1*0301-DQB1*0303 were significantly higher in diabetic patients. The presence of non-aspartic acid at position 57 of the DQ beta-chain was not associated with susceptibility to IDDM. However, the frequency of Arg 52 homozygotes was significantly higher in diabetic patients. These results suggest a role of the MHC molecule and also suggest racial differences in susceptibility to IDDM even within the Asian populations.

Evaluation of premature senescence and senescence biomarkers in carcinoma cells and xenograft mice exposed to single or fractionated irradiation

The purpose of the present study was to elucidate whether premature senescence contributes to the outcome of radiotherapy (RT) and to validate senescence biomarkers in vitro and in vivo. Cultured human cancer cell lines and xenografted mice were exposed to single (SR; 2, 6 or 12 Gy) or fractionated radiation (FR; 3 x 2 Gy or 6 x 2 Gy), and premature senescence was assessed using senescence-associated β-galactosidase (SA-β-Gal) activity, hypophosphorylation of pRb and p21 accumulation. A variety of senescence-associated biomarkers including cathepsin D (CD), the eukaryotic translation elongation factors eEF1A1, eEF1B2, decoy receptor 2 and Dec1 were further validated in vivo or in vitro. We demonstrated the beneficial tumor suppressive role of ionizing radiation (IR)-induced premature senescence in vitro and in vivo. FR inhibited tumor growth via induction of premature senescence as effectively as an equivalent SR dose (≥6 Gy). In addition, CD and eEF1 were valuable biomarkers of cellular senescence in either SR- or RF-exposed carcinoma cells or xenograft mice. Our results suggest that 2 Gy of a conventional RT regime could achieve a better clinical outcome if premature senescence could be increased through an improved understanding of its molecular action mechanism.

ASSESSMENT OF DIAGNOSTIC MULTILEAF COLLIMATOR FOR CEPHALOMETRIC EXPOSURE REDUCTION USING OPTICALLY STIMULATED LUMINESCENT DOSEMETERS

A diagnostic multileaf collimator (MLC) was developed for diagnostic radiography dose reduction. Optically stimulated luminescent dosemeters (OSLDs) were used to evaluate the efficacy of this device for dental radiography cephalometric exposure reduction. The OSLD dosimetric characteristics for 80 kVp cephalometric exposure were first obtained. The batch homogeneity and reproducibility were 1.67 % and 0.18-1.58, respectively. Good linearity was obtained between the OSLD dose and response, and the angular dependence was within ±4 %. The equivalent organ doses for the left eye, right eye and thyroid were 41.20±6.58, 178.86±1.71 and 171.12±8.78 μSv and 36.80±0.33, 156.63±0.22 and 22.04±0.13 μSv for the open and MLC fields, respectively. The MLC-induced dose reductions for the left and right eyes of in field were 10.67±16.78 and 12.42±8.84 %, respectively, and that of the thyroid gland of out of field was 87±8.82 %, considering combined uncertainty. Therefore, use of diagnostic MLC for dose reduction during dental radiography cephalometric exposure is both feasible and effective.

COMPARISON OF SURFACE DOSES FROM INDIRECT AND DIRECT DIGITAL RADIOGRAPHY USING OPTICALLY STIMULATED LUMINESCENCE DOSEMETERS

An optically stimulated luminescence dosemeter was used to compare the surface dose to both eyes from an X-ray delivered frontally to the skull, and the dose could be reduced depending on image acquisition. The detectors were analysed in advance according to each image acquisition method, and the irradiation condition (mA) was obtained to equate the detective quantum efficiency of the two detectors. The surface doses to both eyes were measured in a human phantom. In the detector using the direct conversion method, the surface doses to both eyes were 0.29 ± 0.01 mSv (Rt. eye) and 0.28 ± 0.01 mSv (Lt. eye). In the detector using the indirect conversion method, the surface doses to both eyes were 0.23 ± 0.01 mSv (Rt. eye) and 0.23 ± 0.01 mSv (Lt. eye). Dose reduction by 18.00 ± 8.9% was permitted by the indirect method as compared with the direct method.

Quantitative Evaluation of Gating Radiotherapy System and Dynamic Tumor Tracking Radiotherapy System Developed at KIRAMS

To quantitatively assess of Gating Radiotherapy (GRT) system and Dynamic Tumor Tracking Radiotherapy (DTTRT) system using MLC developed at KIRAMS (Korea Institute of Radiological & Medical Sciences) and evaluate effectiveness and efficiency of beam delivery for the both RT system. DTTRT system resulted to same treatment effect compared with the GRT system controlled with the gating rate of 20%. However, when treat by applying lower gating rate for the GRT system, longer treatment time give inconvenience to patients and cause obstacle to effective utilization of the equipment. On the one hand, DTTRT system presents advantage to reduce treatment time and to achieve effective dose delivery.